A relativistic electron beam, generated by relativistic
self-focusing of an ultra-high-intensity laser pulse in a He
gas jet, was targeted onto high-Z materials for conversion to
high-energy bremsstrahlung. Nuclear reactions in the primary
converter materials as well as in secondary and tertiary targets
placed directly behind the converter were analyzed with
time-resolved γ-spectroscopy. The electron-jet temperature of
more than 35 MeV, matching the giant dipole resonances of
heavy nuclei, enabled us to efficiently generate photo-induced
nuclear reactions. The measured temperatures are significantly
higher than suggested by ponderomotive scaling. We supplemented
our earlier measurement of the (γ, n) reaction cross
section of 129I with a method solely based on nuclear reactions.
The photo-induced transmutation yields were increased
by two orders of magnitude compared to earlier experiments.
Simulations with the Monte Carlo code MCNPX confirm the
experimental results.
PACS 52.38.Ph; 25.20.Lj